Blockcopolymer compositions, having improved mechanical properties and processability and styrenic blockcopolymer to be used in them

ABSTRACT

A composition to be used for the manufacture of fibers, filaments, melt blown or spun bond non-wovens or cast or blown films, comprising at least 50 wt % of a styrenic block copolymer; a polyolefin in an amount of from 10 to 30 wt %; a resin which is compatible with the poly(styrene) blocks in the styrenic block copolymer in an amount of at least 5 wt %, and a resin which is compatible with the hydrogenated polybutadiene blocks in the styrenic block copolymer an amount of at least 3 wt %, wherein all weight percentages are relative to the weight of the complete composition; styrenic block copolymers to be used therein; and fibers, melt blown or spun bond non-wovens or cast or blown films prepared from it.

FIELD OF THE INVENTION

The invention relates to blockcopolymer compositions with improvedmechanical properties and processability and to modified styrenicblockcopolymer to be used in them.

In particular, the invention relates to compositions comprising amodified hydrogenated styrene butadiene blockcopolymer, to be used forthe manufacture of fibers, filaments, melt blown or spun bond non-wovensor cast or blown films.

BACKGROUND OF THE INVENTION

Elastomeric compounds which can be easily extruded, spunbond or meltblown into elastic fibers or films having low stress relaxation, lowhysteresis or permanent set, and high recoverable energy are describedin U.S. Pat. Nos. 4,663,220, 4,789,699, 4,970,259, 5,093,422, 5,705,556and many others. The elastomeric fibers or films are useful in making avariety of applications such as diaper waistbands and non-woven fabrics.

Polystyrene-poly(ethylene-butylene)-polystyrene elastomeric blockcopolymers have been compounded with other materials such as, forexample, polyolefins and tackifying resins to form extrudableelastomeric compositions which can be more easily extruded into elasticfibers or films having improved processing and/or bonding properties.Processes for making cast extruded films, extrusion blown films,extruded fibers, filaments, non-wovens and such like have highrequirements around viscosity of the compound. At the same time,applications of these extrudates in personal hygiene, food wrapping andthe like result in stringent requirements on mechanical behavior; acombination of stiffness (high modulus), and excellent elasticity (goodstress-relaxation and low hysteresis and permanent set) is needed. Oneof the greatest challenges in this field is to find a good balancebetween flow/viscosity and the mechanical properties mentioned above.

It is an object of the present invention to provide compositions thathave excellent balance of properties in personal hygiene applications(fibers, filaments, non-wovens or cast or blown films).

SUMMARY OF THE INVENTION

Accordingly a composition is provided, which can be used for themanufacture of fibers, filaments, melt blown or spun bond non-wovens orcast or blown films, comprising at least 50 wt % of a styrenic blockcopolymer having a molecular structure according to the general formulaeS−EB−S(1) or (S−EB)_(n)X(2),wherein each S

independently is a polymer block of predominantly styrene and EB is ahydrogenated polymer block of predominantly butadiene, n is an integerequal to or greater than 2, and X is the residue of a coupling agent,having a poly(styrene) content in the range of from 10 to 29% by weight(wt %), preferably from 17 to 24 wt %, having poly(styrene) blocks (S)of an apparent molecular weight in the range of from 6,000 to 9,000 andpreferably from 7,000 to 8,500, having an apparent molecular weight ofthe complete block copolymer in the range of from 80,000 to 150,000,having an 1,2 addition degree (vinyl content) in the precursor of thepoly (butadiene) block (EB) in the range of from 60 to 80% (mole/mole),wherein the block EB has a hydrogenation degree of at least 80% andpreferably at least 90%, and wherein diblock S−EB optionally occurs in acontent of at most 20 mole % and preferably at most 10 mole %; apolyolefin in an amount of from 10 to 30 wt %; a resin which iscompatible with the poly(styrene) blocks in an amount of at least 5 wt%, and a resin which is compatible with the hydrogenated polybutadieneblocks in an amount of at least 3 wt %, wherein all weight percentagesare relative to the weight of the complete composition.

In addition modified styrenic block copolymers are provided which havebeen found to be in particular suitable in the compositions for themanufacture of fibers, filaments and melt blown or spun bond non-wovensor cast or blown films. Said products are applied for personal hygieneapplications.

Accordingly styrenic block copolymers are provided to be used incompositions for the manufacture of fibers, filaments, melt blown orspun bondnon-wovens, wherein

-   i. the poly(styrene) content (PSC) is from 17 to 24 wt %,-   ii. the styrenic block copolymer has a molecular structure according    to the general formulae    S−EB−S(1) or (S−EB)_(n)X(2),    wherein each S independently is a polymer block of styrene and EB is    a hydrogenated polymer block of butadiene, n is an integer equal to    or greater than 2, and X is the residue of a coupling agent,-   iii. the apparent molecular weight of the poly(styrene) blocks (S)    is in the range of from 7,000 to 8,500,-   iv. the apparent molecular weight of the complete styrenic block    copolymer is in the range of from 80,000 to 150,000,-   v. the 1.2 addition degree (vinyl content) in the precursor poly    (butadiene) block (EB) precursor is in the range of from 60 to 80    (mole/mole),-   vi. the block EB has a hydrogenation degree of at least 80% and    preferably of at least 90%, and-   vii. an optional diblock S−EB content of at most 20 mole % and    preferably of at most 10 mole %, relative to the total block    copolymer amount.

DETAILED DESCRIPTION OF THE INVENTION

Compositions according to the present invention comprise at least 50 wt% of at least one block copolymer, derived from predominantly styreneand predominantly butadiene.

Preferably said compositions comprise said block copolymer(s) in weightproportions of from 50 to 70 wt % and more preferably from 55 to 65 wt%.

Said compositons comprise in addition to the block copolymer apolyolefin in a weight proportion of from 10 to 30 wt % and preferablyof from 15 to 20 wt %; a polystyrene block compatible resin in a weightproportion of at least 5 wt % and preferably of from 5 to 15 wt % andmore preferably from 8 to 12 wt %; and at least 3 wt % of a hydrogenatedpolybutadiene compatible resin, preferably of from 3 to 10 wt % and morepreferably of from 5 to 10 wt %, relative to the weight of the totalcomposition.

With the terms “predominantly styrene” and “predominantly butadiene”respectively, as used throughout the specification, are meant that forthe respective blocks to be prepared, substantially pure styrene ormixtures comprising at least 95 wt % of styrene and minor amounts ofother comonomers can be used, and substantially pure butadiene ormixtures comprising at least 95 wt % of butadiene and minor amounts ofother comonomers, can be used.

The small proportions of other comonomers in the polystyrene blocks canconsist of structurally related comonomers such as alpha-methyl styrene,p-methyl styrene, o-methyl styrene, p-test.butyl styrene, dimethylstyrene and vinyl naphthalene, or butadiene.

The small proportions of other comonomers in the poly(butadiene) blockcan consist of isoprene or styrene.

However, preferred block copolymers to be applied according to thepresent invention, contain blocks of substantially pure styrene andsubstantially pure butadiene.

The block copolymer according to the present invention may be branchedor linear and may be a triblock, tetrablock or multiblock.

It has a structure represented by the following general formulaeS−EB−S(1) or (S−EB)_(n)X(2)wherein each S independently is a polymer block predominantly styrene,and EB is a hydrogenated polymer block of predominantly butadiene,having a hydrogenation degree of at least 80%, preferably at least 90%and more preferably more than 95%, wherein n is an integer equal to orgreater than 2 and wherein X is the residue of a coupling agent.

The polymer blocks S have an apparent molecular weight in the range offrom 6,000 to 9,000 and preferably from 7,000 to 8,500.

In the block copolymers according to the present invention, the PSC isin the range of 10-29% w, preferably 17-24% w based on the total blockcopolymer. The 1,2 addition (vinyl content) in the midblock precursor isin the range of 60 to 80%, preferably in the range of 65 to 75%.

The complete block copolymers according to the present invention eachpreferably have a total apparent molecular weight (Mw, determined by GelPermeation Chromatography and expressed in terms of polystyrene) rangingfrom 80,000 to 150,000, preferably from 100,000 to 120,000 (using themethod described by J. R. Runyon et al in J. Polym. Sci., 13, 2359(1969)).

The block copolymers according to the present invention can be made e.g.by coupling living diblock copolymer prepared by anionic polymerizationwith a coupling agent or by sequential polymerization. The latter ispreferred.

It will be appreciated thet block copolymers, prepared by means ofcoupling of living diblock copolymers by means of a coupling agent andtermination of remaining living block copolymers, will finally containsmall amounts (i.e. less than 20 mole % and preferably less than 10 mole%) of diblock copolymer, having the same S blocks (mole % relative tothe weight of the total block copolymer).

Preferred block copolymers to be used in the compositions of the presentinvention do not contain any detectable amount of diblock copolymer.

As examples of the coupling agent may be mentioned tin coupling agentssuch as tin dichloride, monomethyltin dichloride, dimethyltindichloride, monoethyltin dichloride, diethyltin dichloride, methyltintrichloride, monobutyltin dichloride, dibutyltin dibromide, monohexyltindichloride and tin tetrachloride; halogenated silicon coupling agentssuch as dichlorosilane, monomethyldichlorosilane,dimethyldichlorosilane,diethyldichlorosilane, monobutyldichlorosilane,dibutyldichlorosilane, monohexyldichlorosilane, dihexyldichlorosilane,dibromosilane, monomethyldibromosilane, dimethyldibromosilane, silicontetrachloride and silicon tetrabromide; alkoxysilanes such astetramethoxysilane; divinyl aromatic compounds such as divinylbenzene endivinyl naphthalene; halogenated alkanes such as dichloroethane,dibromoethane, methylene chloride dibromomethane, dichloropropane,dibromopropane, chloroform, trichloroethane, trichloropropane andtribromopropane; halogenated aromatic compounds such as dibromobenzene;epoxy compounds such as the diglycidyl ether of bisphenol-A (e.g. EPON825, a trademark), and other coupling agents such as benzoic esters,CO₂, 2-chloroprene and 1 chloro-1,3-butadiene. Of these EPON 825,dibromobenzene, tetramethoxysilane and dimethyldichlorosilane arepreferred.

The anionic polymerization of the conjugated diene hydrocarbons istypically controlled with structure modifiers such as diethyl ether orethyl glyme (1,2-diethoxyethane), to obtain the desired amount of1,2-addition. As described in Re 27,145 which is incorporated byreference herein, the level of 1,2-addition of a butadiene polymer orcopolymer can greatly affect elastomeric properties after hydrogenation.The 1,2-addition of butadiene polymers significantly and surprisinglyadditionally influences the polymer as described above. More inparticular, a 1,2-addition of 78% (within the scope of this invention)is achieved during polymerization by the presence of about 300 ppm of1,2-diethoxypropane (DEP) in the final solution.

In general, the polymers useful in this invention may be prepared bycontacting the monomer or monomers with an organoalkali metal compoundin a suitable solvent at a temperature within the range from −150° C. to300° C., preferably at a temperature within the range from 0° C. to 100°C. Particularly effective polymerization initiators are organolithiumcompounds having the general formulaRliwherein R is an aliphatic,cycloaliphatic, alkyl-substitutedcycloaliphatic, aromatic or alkyl-substituted aromatic hydrocarbonradical having from 1 to 20 carbon atoms of which sec.butyl ispreferred.

Suitable solvents include those useful in the solution polymerization ofthe polymer and include aliphatic, cycloaliphatic, alkyl-substitutedcycloaliphatic, aromatic and alkyl-substituted aromatic hydrocarbons,ethers and mixtures thereof. Suitable solvents, then, include aliphatichydrocarbons such as butane, pentane, hexane and heptane, cycloaliphatichydrocarbons such as cyclopentane, cyclohexane and cycloheptane,alkyl-substituted cycloaliphatic hydrocarbons such as methylcyclohexaneand methylcycloheptane, aromatic hydrocarbons such as benzene and thealkyl-substituted hydrocarbons such as toluene and xylene, and etherssuch as tetrahydrofuran, diethylether and di-n-butyl ether. Preferredsolvents are cyclopentane or cyclohexane.

It will be appreciated that the EB blocks in the finally applied blockcopolymers preferably have been selectively hydrogenated to a degree ofat least 95%, whereas the poly(styrene) blocks have not beenhydrogenated or only in a degree of at most 5%.

The hydrogenation of these polymers may be carried out by a variety ofwell established processes including hydrogenation in the presence ofsuch catalysts as Raney Nickel, noble metals such as platinum andpalladium and soluble transition metal catalysts. Suitable hydrogenationprocesses which can be used are ones wherein the diene-containingpolymer or copolymer is dissolved in an inert hydrocarbon diluent suchas cyclohexane and hydrogenated by reaction with hydrogen in the presentof a soluble hydrogenation catalyst. Such processes are disclosed inU.S. Pat. Nos. 3,113,986, 4,226,952 and Reissues 27,145, the disclosureof which are herein incorporated by reference. The polymers arehydrogenated in such a manner as to produce hydrogenated polymers havinga residual unsaturation content in polydiene blocks of less than 5percent by weight, preferably less than 1% wt and more preferably asclose to 0 percent as possible, of their original unsaturation contantprior to hydrogenation. A titanium catalyst such as disclosed in U.S.Pat. No. 5,039,755, which is herein incorporated by reference, may alsobe used in the hydrogenation process.

The finally applied selectively hydrogenated block copolymers can alsoconsist of mixtures of linear block copolymers or of mixtures of linearblock copolymer and branched block copolymers.

The polyolefin used in the compositions of the present invention ispreferably polypropylene (PP) or polyethylene (PE), more preferably ahigh MFR PP (i.e., having a melt flow rate as determined at 230° C./2.16kg, in accordance to ASTM D1238-95 of greater than 400 gr/10 min.).Suitable polyolefins having an MFR of about 800 gr/10 min are “VALTEC”HH442 or “MOPLEN” HF568 by Basell (trademarks), “BORFLOW” HL508 byBorealis and “MIRAEPOL PA189V” by PolyMirae (trademarks). The polyolefinis preferably used in an amount of from 15 to 25% w (on the totalcompound).

The polystyrene block compatible resin may be selected from the groupconsisting of coumarone-indene resin, polyindene resin, poly(methylindene) resin, polystyrene resin, vinyltoluene-alphamethylstyrene resin,alphamethylstyrene resin and polyphenylene ether, in particularpoly(2,6-dimethyl-1,4-phenylene ether). Such resins are e.g. sold underthe trademarks “HERCURES”, “ENDEX”, “KRISTALLEX”, “NEVCHEM” and“PICCOTEX”. A very suitable resin is “KRISTALLEX” F-100. The compoundpreferably comprises from 8 to 12% w of the polystyrene block compatibleresin.

Resins compatible with the hydrogenated polybutadiene (mid)block may beselected from the group consisting of compatible C₅ hydrocarbon resins,hydrogenated C₅ hydrocarbon resins, styrenated C₅ resins, C₅/C₉ resins,styrenated terpene resins, fully hydrogenated or partially hydrogenatedC₉ hydrocarbon resins, rosins esters, rosins derivatives and mixturesthereof. These resins are e.g. sold under the trademarks “REGALITE”,“REGALREZ”, “ESCOREZ” and “ARKON”. A very suitable resin is “REGALITE”R-1125. The compound preferably comprises from 5 to 10% w of the(mid)block compatible resin.

It will be appreciated that another aspect of the present invention isformed by the fibers, filaments, melt blown or spun bond non-wovens orcast or blown films, obtained by processing the hereinbefore definedcompositions.

A further aspect of the present invention is formed by the specificblock copolymers to be used in the compositions for the manufacture offibers, filaments, melt blown or spun bond non-wovens or cast or blownfilms.

The compositions of the embodiments may contain a plasticizer. However,as plasticizers have the tendency to migrate, their presence istypically to be avoided.

Other ingredients may be incorporated into the compositions according tothe present invention. For instance, processing aids can be added orcolorants, as well as antioxidants and other stabilizing ingredients toprotect the compounds from degradation induced by heat, light andprocessing or during storage.

Preparation of the Composition

No particular limitation is imposed on the preparation process of thecompound of the present invention. Therefore, there may be used anyprocess such as a mechanically mixing process: e.g., a Banbury mixer ora twin-screw extruder provided with adequate mixing elements, therebyobtaining an intimate mixture of the ingredients.

Use of the Composition

Compositions according to the present invention may be applied, e.g. byextrusion, for the preparation of fibers, filaments and melt blown orspun bond non-wovens or cast or blown films.

The present invention will hereinafter be described more specifically byreference to the following examples and comparative examples. However,this invention is not limited to these examples only. Incidentally, alldesignations of “part” or “parts” and “%” as will be used in thefollowing examples mean part or parts by weight and percentage by weightunless expressly noted. The measurements of physical properties wereconducted in accordance with the following methods.

Test Methods

-   -   melt flow rate (MFR): ASTM D1238-95 (230° C., 2.16 kg)    -   tensile properties on fibers:    -   hysteresis: strands produced by melt index tester are clamped in        a mechanical tester (Zwick). Strands are elongated to 150%        extension at a speed of 100 mm/sec (load step), and immediately        relaxed to zero force (unload step). A second cycle follows        right after the first one. Forces at 50 and 100% elongation are        recorded for the first cycle. Hysteresis is measured as the        difference in energy between the load and the unload step.        Permanent set is measured as the difference between the original        sample length of the first cycle (force equals zero) and the        sample length before the second cycle (force equals zero).    -   stress-relaxation: strands produced by melt index tester are        clamped in a mechanical tester (Zwick). Strands are elongated to        50% extension, in a hot-air oven at 40° C. The samples are held        in that position for 2 hrs. The force decay is measured. The        stress-relaxation is expressed as the ratio between the final        force and the initial force (equaling the percentage of retained        stress).

tensile properties according to ASTM D882-81 (tested on films) TABLE 1(ingredients) Styrenic Block copolymers: SBC A A linear SEBS having adiblock content of about 30%; a comp. PSC of 13.3%, a MW (PS) of about5,300; an apparent MW of about 145,000 and a vinyl content of 45% SBC BA linear SEBS having a PSC of 21%, a MW (PS) of about 8,000; an apparentMW of about 115,000 and a vinyl content of 65% SBC C A linear SEBShaving a PSC of 20.5%, a MW (PS) of about comp. 10,000; an apparent MWof about 150,000 and a vinyl content of 68% SBC D A linear SEBS having aPSC of 30%, a MW (PS) of about comp 7,000; an apparent MW of about80,000 and a vinyl content of 40% Polyolefins: HF568X “VALTEC” HH442H or“MOPLEN” HF568X, a PP having an MFR of 800 g/10 min and a Modulus of1500 MPa PA189V “MiraePol” PA189V, a PP having an MRF of 900 g/10 minEndblock compatible resins: F-100 “KRISTALLEX” F-100; analpha-methylstyrene resin Midblock compatible resins R-1125 “REGALITE”R-1125; a fully hydrogenated C9 hydrocarbon resin

EXAMPLES 1-6

Compositions for the preparation of fibers, non-wovens use were preparedon a 25 mm Werner & Pfleiderer ZSK25 co-rotating twin-screw extruderwith 49 L/D. The ingredients from Table 1 were pre-blended according tothe amounts in Table 2 in a Papenmeier internal mixer, and fed into onefeeding port. Strands were cooled in a water-bath and granulated using astrand-cutter.

Strands were prepared with a Gottfert melt index tester as described inASTM D-1238-95. The mechanical properties of these strands weremeasured, and the results are included in Table 2. TABLE 2 compositionExamples 1 2 3 4 5 6 SBC A comp 65 SBC B 60 65 65 SBC C comp 65 SBC Dcomp 65 HF568x 20 15 20 20 20 20 F-100 10 10 10 10 10 10 R-1125 10 10 55 5 5 Properties MFR (g/10 min) 49 37 30 27 11 1.5 Stress n.m 42 40 3841 56 Relaxation (%) Permanent 17 12 14 24 23 11 Set (%) Modulus 50%3.17 2.32 3.18 2.64 4.31 2.16

Conclusion

The compound of Example 3 is based on the right polymer at the rightamount. Accordingly, it has the right balance of properties. On theother hand, the compound of Example 1 has a very high MFR and a highmodulus, but a permanent set that is too high. The compound of Example 2has a good MFR and elasticity (stress-relaxation and permanent set), buta high flow and a too low modulus.

In Example 4 the composition has a good flow, but a too low modulus andno elasticity (bad hysteresis and stress-relaxation).

In Example 5 the composition has a very high modulus, a too low flow,and no elasticity (bad hysteresis; the stress-relaxation is acceptable).

In Example 6, the composition shows a very good elasticity (hysteresisand stress-relaxation) but a too low modulus and a very poor flow.

1-10. (canceled)
 11. A styrenic block copolymer, wherein the copolymercomprises: i. a poly(styrene) content (PSC) of from 17 to 24 wt %; ii. amolecular structure according to the general formula:S−EB−S (1) or (S−EB)_(n)X (2),  wherein each S independently is apolymer block of styrene and EB is a hydrogenated polymer block ofbutadiene, n is an integer equal to or greater than 2, and X is theresidue of a coupling agent; iii. an apparent molecular weight of thepoly(styrene) blocks (S) in the range of from 6,000 to 9,000; iv. anapparent molecular weight of the complete styrenic block copolymer inthe range of from 80,000 to 150,000; V. a 1,2-addition degree (vinylcontent) in a precursor poly (butadiene) block (EB) precursor in therange of from 60 to 80 (mole/mole); vi. the block EB has a hydrogenationdegree of at least 80%, and vii. an optional diblock S−EB content of atmost 20 mole %, relative to the total block copolymer amount.
 12. Thestyrenic block copolymer of claim 11, wherein the apparent molecularweight of the poly(styrene) blocks (S) in the range of from 7,000 to8,500.
 13. The styreneic block copolymerof claim 11, wherein thehydrogenation degree of the EB block is at least 90%.
 14. The styrenicblock copolymer of claim 11, wherein the hydrogenation degree of the EBblock is at least 95%.
 15. The styrenic block copolymer of claim 14,wherein the 1,2-addition degree in the EB block is in the range of from65 to 75%.
 16. The styrenic block copolymer of claim 11, wherein theapparent molecular weight of the styrenic block copolymer is in therange from 100,000 to 120,000.
 17. The styrenic block copolymer of claim13, wherein the apparent molecular weight of the styrenic blockcopolymer is in the range from 100,000 to 120,000.
 18. The styrenicblock copolymer of claim 14, wherein the apparent molecular weight ofthe styrenic block copolymer is in the range from 100,000 to 120,000.